PROTRUSION OF THE ICA INTO THE SPHENOID SINUS

Author(s)

Basekim CC, Ozturk E

Patient

female, 75 year(s)

Clinical History

An anatomic variation of sphenoid sinus was presented.

Imaging Findings

The patient presented with nasal discharge and intermittent headache for two weeks. The computed tomography (CT) scans of the paranasal sinuses revealed mucosal thickening of bilateral ethmoidal
cells and left compartment of the sphenoid sinuses on both axial and coronal planes. The right internal carotid artery (ICA) protruded into the sphenoid sinus cavity and the sinus wall adjacent to
the groove for the right ICA was quite thin. The relationship between the ICA and sphenoid sinus was normal on the left side.

Discussion

There is a wide range of anatomic variation in sphenoid sinus development, especially in the relationship of the neighboring structures. It has been said that the sphenoidal sinus was the most
variable in form of any bilateral cavity or organ in the human body. ICA is one of the neighboring structures of the sphenoid sinus. It courses through the area surrounded by bony structures such as
sphenoid sinus wall or clinoid processes. In some instances, the bony plate separating the sphenoidal sinus from the ICA may be very thin or absent. Hence it may become vulnerable in chronic sinus
infections. The bony dehiscence can be explained with indentation of the sinus wall by the ICA or partial volume effects at sites in which the normal but thin sinus wall has an oblique course through
the imaging plane. Protrusion of the ICA into the sphenoid sinus is one of the common anatomic variations of the sphenoid sinus. In the literature, the reported rate of the intrasphenoid protrusion
of the ICA varies between 8% and 26.1%. The grade of protrusion increases, as the sinus grows larger. When the sphenoid sinus is highly pneumatized, the ICA can course freely through the sphenoid
sinus cavity. It has been reported that the incidence of bilaterally protruding ICA is higher than the incidence of unilaterally protruding ICA. Intrasphenoid prolapse of the ICA is a major risk
factor in endoscopic sinus surgery. The high incidence is required routine preoperative CT imaging to reduce surgical risk.